1. Field of the Invention
The present invention generally relates to a method of detecting protrusion of an inspection object from a palette, and more specifically, it relates to a method of detecting protrusion of an inspection object from a palette improved to be capable of remarkably widening a determination margin and implementing stable detection. The present invention also relates to a method of fabricating a semiconductor device comprising such a method of detecting protrusion of an inspection object from a palette.
2. Description of the Prior Art
A conventional semiconductor tester brings leads of integrated circuits (hereinafter abbreviated as ICs) into contact with electrodes provided in sockets, for testing electric characteristics of the ICs. In order to transport workpieces (ICs) in the semiconductor tester, a magazine containing stacked pallets, dedicated to transportation, storing ICs is set on an in-loader so that the palettes are sliced from the in-loader one by one and horizontally transported to a test part.
The ICs are tested by bringing the leads thereof into contact with the electrodes provided in the sockets. In this method, the ICs stored in each palette are pushed up and brought into contact with the sockets arranged above the palette. The sockets are arranged upward, to be prevented from collecting solder residues. Further, cooling air or hot air is blown to the test part for maintaining the environmental temperature in the test. The test part is provided in an adiabatic vessel, for circulating the air.
FIG. 10 is a block diagram of a conventional semiconductor tester 11 having the aforementioned test part.
Referring to FIG. 10, ICs 1 are placed on push-up parts 4 for pushing up the ICs 1 toward sockets 5. A transport palette 2 horizontally transports the ICs 1. A cooling air generator 10 introduces cooling air 6 into a test part 3. A magazine 12 is inserted in an in-loader 8, so that the ICs 1 pass through an IC protrusion detection part 13. The ICs 1 tested by the tester 11 are transferred to an out-loader 9.
In the aforementioned structure of the test part 3, any IC 1 may protrude from a pocket of the transport palette 2 to cause displacement and two ICs 1 may overlap with each other in the same pocket as shown in FIG. 11, to unstabilize contact between the leads of the ICs 1 and socket electrodes and hinder a normal test.
In this case, the protruding and overlapping ICs 1 may break the push-up parts 4 and the sockets 5 as shown in FIG. 12, to disadvantageously reduce workability of the overall tester 11 and deteriorate productivity.
Therefore, it is necessary to detect whether or not the ICs 1 are normally stored in the pockets of the transport palette 2 immediately before testing the same in the test part 3.
FIG. 13 shows a conventional detection method employing a lever-type detection mechanism. In this lever-type detection mechanism, the transport palette 2 transports the ICs 1 along arrow 15. A protrusion detection lever 16 is fixed to a limit sensor 18 through a support point 17.
However, this method can detect no IC 1 protruding from the pocket storing the same, and is insufficient in function.
FIG. 14 illustrates another conventional method employing an optical sensor type detection mechanism.
Referring to FIG. 14, the ICs 1 are placed on the transport palette 2 and transported along arrow 15. Reflection type photoelectric sensors 19 are connected to a controller 31 through sensor amplifiers 30. While this method can detect any IC 1 protruding from the pocket storing the same, a threshold for determining defectiveness/non-defectiveness is set between the lower limit for defectives and the upper limit for non-defectives for making detection in units of ICs by comparing absolute values. Therefore, the margin for setting the threshold is disadvantageously reduced while reflection levels on the surfaces of the ICs 1 vary with the types of the ICs 1. The latter problem results from difference between molds varying with the types of the ICs 1 and the degrees of soiling of the molds. Therefore, it is difficult to make stable and precise detection by this method due to remarkable dispersion.